Preimage and collision attacks on reduced Ascon using algebraic strategies

Abstract Ascon, a family of algorithms that supports hashing and authenticated encryption, is the winner of the NIST Lightweight Cryptography Project. In this paper, we propose an improved preimage attack against 2-round Ascon-XOF-64 with a complexity of $$2^{33}$$ 2 33 via a more effective guessing strategy. Furthermore, we successfully extend our preimage attack on 2-round Ascon-XOF-64 to 2-round Ascon-XOF-128, achieving a complexity of $$2^{97}$$ 2 97 , which is currently the best preimage attack against 2-round Ascon-XOF-128. Apart from the preimage attack, we also investigate the resistance of Ascon-HASH against collision attacks. To be specific, we introduce the linearization of the inverse of S-boxes and then propose a free-start collision attack on 3-round Ascon-HASH with a complexity of $$2^{14}